单项选择题
A.0.1s B.0.2s C.0.5s D.1s
A.10％一15% B.15％一20% C.20％一40% D.50％一60%
A.0.02一0.04s B.0.01一0.03s C.0.04一0.06s D.0.05一1s
A.5% B.10% C.15% D.20%
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